My problem is that I'm not receiving or getting delayed push notification on my Nexus 4

Firstly I thought it was a 3g issue and switch to WiFi (no luck)... the problem is, sometimes I don't receive whatsapp notifications while my phone is "sleeping" I need to open the whatsapp to receive the message in my phone, i receive all messages together when I open the app, it wasn't like this before....

Does anyone knows why? I was using Cyanogen M4 before and getting this same problem sometimes

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